Replacing the iridium spark plugs

[cc]

Hi
Have done over 50,000km on the plugs in the 2002 V6 156..  and is still running ok. they are about 3 years old.
Has anyone had any issues not replacing them? at 50 000km.
Have noticed a white powder just starting on the inside of the exhaust pipe. An alfa mechanic said this may be due to a tank of 95 octane non BP fuel..
cheers CC

[Mick A]

The plugs don't need to be changed until 100,000km!

Keep on thrashing it!

[cc]

will do. Might just have a look at them and also do a compression check.